I have personally used it; not much of a change in battery life, performance was a little better. The big difference comes from running thie, using setcpu to performance and using the one click lag fix from market to really make my phone sing. However when running it in performance mode in setcpu, I only get 4-5 hours of battery life.

How does the lag fix kill the SD card? This is the 1st time I'm seeing anything about that.

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Most of the lag fixes, from what I understand, create a Linux ext2/3 filesystem somewhere and use that to store important files, bypassing Samsung's own filesystem, which is slower. But ext2/3 are designed for hard drives, not flash memory, which is what's on an SD card (and the Captivate's internal storage). Flash memory can only be written to a limited number of times before it wears out. I don't really know anything about Samsung's filesystem here, but I infer that theirs does wear-leveling to avoid this problem (otherwise, why would they have bothered to write their own filesystem and not just use ext2/3 which were already available?). IOW, if you save a file, then delete it, then save another, ext2/3 would likely write the new file in the same spot where the old one was, if it fits. On an actual hard drive, this doesn't matter. But if you do this repeatedly on flash memory, that location will get worn out while other locations remain unused. And eventually you'll get data corruption as the worn locations can't retain what's written to them anymore. A flash-aware wear-leveling filesystem on the other hand will write the new file to a fresh location, causing everything to wear at an even rate, so the whole card fails at the same time. And the failure will happen later, unless you keep the card completely full all the time. This is *presumably* why Samsung didn't just use ext2/3 in the first place.

So, you may ask (being the clever sort that you are ), what about all the people running Linux on desktop/laptop machines with SSDs? Aren't those flash-based, and aren't those people just running ext2/3? Yes, and yes, but an SSD has its own firmware which does the wear-leveling itself, while letting the filesystem above it think it's doing what it always did. An SD card just ain't that smart.

That's the theory anyway. Whether any of this matters in practice, I don't really know. After all, your Captivate really only has to last until you're eligible for your next subsidized upgrade, at which point you'll be getting that new 1.5GHz dual-core processor phone (and a new SD card). Right?

Most of the lag fixes, from what I understand, create a Linux ext2/3 filesystem somewhere and use that to store important files, bypassing Samsung's own filesystem, which is slower.

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Some redo the data partition into a new filesystem, while others lay on a virtualized ext2/3/4 layer on top of the original RFS filesystem.

But ext2/3 are designed for hard drives, not flash memory,

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Not really correct. Ext2/3/4 are not specifically designed for any certain media type.

Flash memory can only be written to a limited number of times before it wears out.

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Technically correct. However you'll be getting a new phone before you wear out your flash.

I don't really know anything about Samsung's filesystem here,

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Well, let me enlighten you. It's called RFS for "robust file system" and it's nothing more than the archaic FAT filesystem with some lame journaling glued on in an inefficient manner so it can claim to be journaled. Unfortunately it's slow as death, but for whatever reason Samsung is proud that they can call it "theirs".

but I infer that theirs does wear-leveling to avoid this problem

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The RFS filesystem doesn't, no. The wear-leveling for flash is performed at the hardware level by modern flash memory controllers. It's filesystem-independent.

(otherwise, why would they have bothered to write their own filesystem and not just use ext2/3 which were already available?).

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RFS is simpler. RFS also uses FAT at its core so it'd work with archaic legacy file-system tools. Really though there's no good reason. RFS is a Samsung creation and it sucks horribly.